Gun construction



A. J. POPE GUN CONSTRUCTION ocf. 15, 1957 3 Sheets-Sheet l Filed June 24, 1950 Snoentor m ART/WR J PoP/E Gttorneg I GUN CONSTRUCTION .Filed June 24, 1950 5 Sheets-Sheet 2 li :a

:Snuentor Afr/fu@ J.' Pope 'Gttomeg 0d. l5, 1957 A. J. POPE 2,809,564

GUN CONSTRUCTION Filed June 24, 1950 3 Sheec'fs-Sheel'l 5 /45 Snventor /46 A67/Ya@ JT POPE 8u @lq/5T W MAM' M Gttorneg United States Patent GUN CONSTRUCTION Arthur J. Pope, Madison, Conn.

Application June 24, 1.950, Serial No. 170,178

4 Claims. (Cl. 89-128) This invention relatesto firearms of the type that utilize a breech block or, bolt that responds to the reaction of the explosive for achieving cyclic actuation of the gun.

One of the objects of this invention is to provide an improved gun of the above-mentioned type that willbe of compact, strong and not unwieldy construction, of smooth and efficient action, and of simple and easy manual selective control.

Another object is to provide an eflicient and reliable receiver and bolt construction, Vaction and assembly in which pneumatic action and spring action combine to give smoothess and ease of gun operation and facilitate coaction with trigger and Sear `for consistently dependable manual selective control. Another object is to provide a sear control and trigger mechanism that will give ease and simplicity of action and selectivity Vfor single re, manual repeat ring, or automatic su-ccessive firing, and also dependable and consistent coaction with the breech block or bolt. Another object is to provide a dependable and rugged sear control and trigger mechanism that is of individually simple parts which are not costly to manufacture and are capable of ready assembly to provide positiveness and ease of manual control and action under the varying conditions of practical use.

Another object is to provide a gun construction of the above-mentioned type with combined pneumatic and spring control of bolt movement and that is simple in construction and action, inexpensive in construction and assembly, that makes for ease and simplicity of construction, that isreliable and consistent in action, that will give smoothness and comfort in handling and operation, and that permits of .long-continued use with minimum of adverse physical reaction of the user. Another object is to provide a gun construction of the abovementioned type in which the mechanism and construction for achieving the above type Vof, spring and pneumatic action facilitateV simplicity of manufacture landconstruction, eXpedite'large-scale production and assembly, avoid such precision of relative dimensioning of parts as militates against inexpensive manufacture, simplicity of maintenance and care, and consistency of performance in practical use. Y

Another object is to provide a gun construction of the above-mentioned character'in which ruggedness and durability of construction are combined with simplicity'of protection Vagainst usual buthard conditions of practical use and with simplicity and ease of use, care, and maintenance.

Other objects will be in part obvious or in part pointed out hereinafter. l

The invention, accordingly, consists in the features of construction, combination of elements, and arrangement of parts as will be exemplified in the structure to be described hereinafter and the scope'of the application of which will be indicated in thefollowing claims.

In the accompanying drawings,in which is shown illustratively one ofthe various possible embodiments of my invention Y Patented Oct. 15, 1957 ICC Figure 1 is a central longitudinal vertical `sectional view Aof a gun construction according to my invention, certain parts being broken away or omitted for greater simplicity of exposition; Y

Figure 2 is an end elevation partly in section as seen along the line 2--2 Vof Figure l, showing also the rear sight and an illustrative hand grip;

Figure 3 is a transverse vertical section as seen along the line 3 3 of Figure 1, showing the relationship between the receiver, the breech block, and other parts for achieving a compound pneumatic action; v

Figure 4 is a horizontal fragmentary sectional view as seen along the line 4-4 of Figures l and 2, showing certain features of the end closure for the receiver and certain features of therear sightmechanism;

Figure 5 is a transverse vertical sectional view on an enlarged scale as seen along the line 5-5 of Figure l, showing certainfeaturesV of the trigger mechanism in its relation to the breech block;

Figure 6 is a transverse vertical sectional View on an enlarged scale as seen along the line 6 6 of Figure 1, showing certain relationships between the bolt and the ejector and showing also certain parts of the trigger assembly;

Figure 7 is a transverse vertical sectional v iew as seen along the line 7-7 of Figure l, showing part of the retractor mechanism; i Y

Figure 8 is a vertical sectional view of a portion of the gun structure Ias seen along the line 8-8 of Figure 7 and showing other features of the retractor mechanism;

Figure 9 is an isometric View on an enlarged scale of a subassembly of the trigger mechanism;

Figure l0 is an isometric view on a much smaller scale Yof `a preferred form of part for closing olf the rear end of the receiver;

Figure 1l is a central longitudinal vertical sectional view on an enlarged scale of the trigger and sear mechanism which is also shown in Figure 1;

Figure l2 is a transverse vertical sectional view as seen along the line 12-12of Figure 11,'showing the mounting of the sear;

Figure 13 is a vertical sectional'view as seen `along the line 13-13 of Figure 11, showing on an enlarged scale a .manually controlled mechanism for setting the range of trigger movement; Y

Figure 14 is a vertical sectional view as seen along the line 14-'14 of Figure 13; and

Figure l5 is a transverse vertical sectional view as seen along the line 15-.15 0f Figure l, showing the gun with a cartridge magazine attached'.

Similar reference characters refer to similar partsV of fabricated tubing of steel or `other suitable material.

At its front end the receiver 10 has tted and secured to it a short and suitably heavy memberV 11, later'described in greater detail, which is provided with any suitable means for attaching thereto a gun barrel l2 which may be rifled and of which only a portion is shown in Figure l. Conveniently, the connection between the member l1 andthevbarrel 12 may be a threaded connection, as indicated at 13, the member 11 being internally bored out and threaded up to an internal annular shoulder 14 and the end of the gun barrel 12 being externally threaded up-to an external annular shoulder 15. These parts may be suitably dimensioned so that when the barrel 12 is threaded into'the mounting member 11, the end of the b-arrel abuts securely against'the internal shoulder 14- and the shoulder 15 of the barrel abuts ightly against Vthe front end -face of the member 11.

These parts are all circular in cross-section, thus facilitating fabrication and assembly, and the relative dimensions are such that the barrel 12 and the mounting member il are coaxial with each other as well as with the tubular receiver 19. receiver l@ and may be secured thereto, as by welding, as indicated at lr6.

Inserted into the rear or left-hand end of the receiver l@ is a breech block generally indicated by the reference character ES and comprising a relatively long, hollow, cylindrical block 19 that iits loosely for sliding move* ment in the receiver and having integrally formed therewith at its right-hand or forward end a bolt 20 for co-action with the cartridges in a manner hereinafter described in detail. The cylindrical block 19 has a long internal bore 2l that is open at its left-hand end and of a diameter and length to leave a mass or Weight of metal in the block i9 which, when added to the Weight or mass of the bolt 2lb, is appropriately related to a propulsion spring 22, later described, to insure a forward motion of the block i8 at sufficient velocity to amply provide the energy needed to inject a cartridge into the rear end of the gun barrel and then also to impact the cartridge to detonate the explosive in the shell and thus propel the projectile along and out of the gun barrel.

A s above noted, the parts 19 and 20 of the breech block or bolt are integral and are preferably formed out of a single piece of metal, and here it is to be noted that relatively simple and inexpensive turning or boring operations sutlce to 4give the parts the desired conformation.

At its right-hand end the bolt 2@ is provided at its center with a tiring pin 23 which is at the axis of the bolt structure and which, as is better shown in Figure 8, projects from the base of a counterbore or turned recess 24 in the end of the bolt 20, the recess 24 being laterally bounded by a flange 25 having suitably curved or shaped internal faces to guide the rear flanged end F of a cartridge C into substantial coaxial relation to the bolt 20 during the injecting stroke of movement of the bolt structure 18. The ilange 25 can also be easily turned.

As will be later explained, a magazine carrying a suitable number of cartridges is carried laterally of the receiver 1th, and for each forward stroke of the bolt 20 the magazine mechanism, through a spring, urges the foremost cartridge in the magazine into the path of movement of the bolt 20 to inject the cartridge into the barrel l2, preferably by structural features and coactions as are later more fully described.

At a suitable location at the forward end of the bolt 2t, the latter is provided with a milled slot 26 in which is seated and mounted in any suitable manner any usual or known form of spring clip 27 appropriately toothed at its outer end, as at 27a, to engage over the peripheral flange F `(see Figure l) of a cartridge C in order to be sure to withdraw or extract the emptied shell S from the gun barrel on the rearward stroke of movement of the block 18.

The empty shell thus carried rearwardly with the bolt 20 is ejected from the gun through a suitable side opening 29 in the receiver, being in effect flipped laterally off the front end of the bolt 20 by an ejector in the form of a relatively heavy pin 30 that is mounted on the inside face of the receiver 10 at an angle to a radius of the latter; the pin 3) is of a radial length sufficient to be in the path of rearward movement of the empty shell as it is carried rearwardly by the bolt 20, the latter having a milled slot 3i of sufficient length and intersecting also the flange 25 at the end of the bolt to accommodate the end of the pin 30 therein during the strokes of movement of the bolt 20. The pin 30 may be mounted on the receiver l@ in any suitable manner, and preferably I provide a mounting member for it in the form of a small tapered stud 32 which may be welded or otherwise secured to the inside face of the receiver 1G. The stud 32 is internally threaded to receive the threaded portion Member l1 tits snugly into the end of the,

4 of the ejector .pin 3i). The relationship of these parts is shown in Figures l and 6.

The detonation of the explosive in the cartridge C impels the projectile P thereof along and out of the barrel i2, and the reaction from that action impels the relatively large mass of the breech block structure 18 rearwardly, or to the left in Figure l, at substantial velocit whereupon, according to certain features of my invention, a number of structural features are brought into coaction to achieve selective control of the ensuing and subsequent operation of the block and bolt structure 19-20. in order to understand these more clearly, it is first to be noted that I provide a relatively large clearance, indicated at 35, between the inside wall of the receiver 10 and the outside cylindrical surface of the block i9, as is clearly shown in Figures l, 2, 5, 7, and 8; this I achieve by making the outside diameter of the block 19 materially less than the inside diameter of the receiver it?, and the large clearance is thus made to form gn air passage that is annular in cross-section.

The bore 21 in the breech block 19 leaves an end annular face 36 at the left-hand or rear end of the block 19, and that end face I cause to coact with certain other parts to serve as an annular piston in an annular chamber, the outer cylindrical wall of which is formed by the receiver 10 and the inner cylindrical wall of which is formed by the outside wall of a tubular part 37 that is formed preferably integrally with and also coaxially with a relatively heavy cylindrical block 38 that tits snugly into and closes the rear end of the receiver 10. The block 3S has integrally formed with it a heavy flange 39 which abuts against the rear end of the receiver 10 and thus fixes the position of the block 38 and also of the tubular part 37 relative to the receiver 10 and other parts, in cluding the breech block structure 18. In Figure l0 is shown in perspective, and indicated generally by the reference character 4u, the unit structure made up of the above-described parts 37, 38, and 39, and aids in indieating how the member 4t) may be inexpensively and speedily constructed, as by turning and boring out of a single piece of metal, the tubular part 37 being bored out, as is better shown in Figure l.

In the solid block 38 of the member 40 there is formed, as by drilling, a hole 41 Whose axis is along a diameter of the block part 38, so that when the member 40 is inserted into the rear end of the receiver 10, the hole il becomes aligned with upper and lower holes 42 and 43 that are diametrically aligned and provided in the walls of the receiver 10 which7 at the rear end portion, may be and preferably are reinforced and made thicker by a band 44 of metal of suitable thickness that extends completely around the receiver. The ring-like band i4 may be shrunk onto the receiver it), or welded or ot erwise secured thereto; it not only strengthens the end portion of the receiver 10, but also materially thickens those diametrically opposed wall portions in which, as shown in Figure l, the holes 42 and 43 are provided.

As is better shown in Figure 2, the heavy band 44 is provided with two spaced depending lugs or ears 45 and 46 having vertical faces that are parallel to each other; the ears 45 and 46 provide between them a parallel-sided slot 47 whose width is at least as great as the diameter of the above-mentioned opposed and aligned holes 42 and i3 and whose median plane is coincident with the common axis of the holes 42 and 43.

T o lock the unitary part 40 in position within the rear end of the receiver 10, l provide a heavy pin or cylindrical stud 5G which passes snugly into the aligned holes 43, 41, and 42 (see Figure l) and which is integrally formed with a relatively heavy shank S1 (Figure 2) that is parallel-sided and snugly receivable at its upper end between the ears 45 and 46. The shank 51 forms or has secured to it any suitable means for mounting or holding the gun and, illustratively, such means may comprise a hand grip generally indicated by the reference character 52 in Fig- L'res rl fand 2; in such'case, the-:hand grip 452 maycomprise suitable, preferably `non-metallic pieces 53, 54 secured to the shank, as `by rivets 55, and being suitablyshaped for convenient gripping bythe hand.

As is better shown in Figures 1 and 2,-the ears 45 and 46 and lthe shank 51 are provided with suitable holes which becomes aligned when the assembly pin or stud 50 is manually forced home, that is, to the position shown in Figure 1, wherein the full extent of entry of the heavy .stud 50 into its aligned holes is fixed or limited by the engagement of the at horizontal face 56. at the upper end of the shank 51 with the under face, appropriately flattened, of the heavy band or ring 44. A bolt 57, provided with Va thumb nut 58, passesthrough the aligned holesin the lugs 45 and 46 and the shank 51, thus hold- `ing `the assembly pin 5t) in locking position and also holding the upper at face 56 of the shank 51 snugly against the under flat face of the band 44; this latter vrelationship aids in protecting the locking stud Silagainst bending strains or stresses that might be caused by the available leverage that might be exerted by way of the shank 51 and, for example, the `illustrative hand grip 52 Y associated with it.

All of the just described parts are inexpensively fabricated and are dimensioned for snug interitting so as to permit of ready and convenient manual assembly or disassembly. v

`inside diameter of thejreceiver 10. The tubular part 37,

therefore, may be relatively thin-walled-*a factor contributing towardlessening the weight ofthe gun construction, but, being tubular in shape, it has adequate and, in fact, substantial strength and, hence, substantial ruggedness and durability. It is closed off at its rear or lefthand end by the cylindrical block part 38 which conveniently forms an abutment for one end of the spring 22 which is of relatively large diameter in relation to the tubular part 37 in which it is received and guided, particularly during those portions of movement of the turns of the spring 22 that correspond to high and maximum spring compression. The other end of the spring 22 abuts against the disk-like face 66 at the inner end of the bore 21 in the breech block 19. In the position shown in Figure l, the breech block and bolt structure 18 is shown in retracted position in which'it is releasably held by a sear 61, later described in detail, and in that position of the parts the spring 22 is compressed and has stored in it sullcient energy which, when released, projects the bolt structure 18 forwardly (to the right in Figure 1) to injecta cartridge into the barrel and also to detonate its charge. The length of the bore 21 in the breech block 19 and the length of the tubular part 37 are such that when the bolt structure `18 is held in retracted position by the sear 61, there exists a substantial space between the end of thev tube part 37 and the end face 60 of the bore 21, thus also to provide sufficient range of movement rearwardly of the bolt structure 13 on its retrograde stroke to make certainthat the breech block 19,l at its right-hand end face, bypasses the sear 61 rearwardly and to give the sear time to snap upwardly into the receiver to catch and hold the breech block at its forward end face, as shown in Figure l.

With the above-described telescopic relationship of the tubular part 37 and the bore 21 of the breech block 19, each with one end closed, I cause them together to form a chamber or cylinder of variable volume, variable according to the position of the breech block 19 in its strokes of reciprocating movement, and, for convenience of description, the inner end face 6i) of the bore 21 may be considered as the piston that operates to -change the volume of this telescoping cylinder. The interior of this Dchamber 'or cylinderof variable volume -I place in continuous communication with the annular space Y Vbetween the block part 38 andthe annular piston 36 formed by the end annular face of the breech block 19, and such communication l prefer to achieve by an annular passage 62 formed between 'the outside cylindrical wall of the tubular part 37 and the inside cylindrical wall of the bore 21, as by making sure that the diameter ofthe latter is sutciently greater that the diameter of the former to provide a Vlarge enough clearance between the two to form the desired annular cross-section of passageway. Figures l, 3,V and 5 show, in somewhat exaggerated form, indicated relationships of the various diameters concerned to provide substantial airways, Vboth at the clearance space 62 and the clearance space 35, and where it is desired that the two airways 35 and 62, both being annular in cross-section, be of substantially the same area, the radial dimension of the airway62, of course, becomes greater than the radial dimension of the airway 55.

With such arrangement of parts as I have just illustratively described, I am enabled to achieve a number of unique and highly advantageous actions and coactions of and between moving parts and related control mechanisms.- In the first place, the relatively large airways in the illustrative embodiment I form out of surfaces which are geometrically simple and inexpensive to form or machine, being turned or bored or drawn, etc. The purposeful large `differences in diameters, for forming these airways, for manufacturing purposes might be considered as exceedingly large clearances; and while I facilitate precision of dimensioning during Vmachining of the individual parts or surfaces, it isto be noted that these large clearances not only facilitate assembly, but completely avoid any need for costly precision or fitting of one part to or into another; no'concern need be given,

for example, to such costly considerations as tolerances necessary for a so-called running lit.

Next I am enabled to achieve almost frictionless movement of the relatively heavy bolt structure relative to both the inside wall of the receiver 10 and the outside wall of the tubular part 37 for the piston and cylinder actions that take place, during both strokes of movement'of the breech block structure 18,'insure movement of air through the annular airways 21 and 35, at suitable relative pressures to virtually float the moving bolt structure on the airstreams flowing through the two airways. Moreover, though the bolt structure l, relatively speaking, isheavy, the two annular airways coact with relatively large areas of surfaces of the block 19 so that small relative air pressures per unit area are usable. Moreover, as better appears from consideration of not only Figure l, but also Figures 3 and 5, the relative air pressures exerted in the annular airways 21 and 35 are in each uniformly distributed relative to the axis of the moving bolt structure and exert thereon a nicely balanced and, in effect, a centering action, tending always to float the moving breech block 19 into,` and tending to maintain it in, coaxial relation with the xed coaxialparts, namely, the receiver 10 and the tubular part 37.

When the bolt structure 18 in Figure 1 is released by the sear'tl, the energy stored in the spring 22 commences to move the bolt structure 18 toward the right, as and for the purposes earlier above described, namely, to inject and detonate a cartridge. Within the telescoping chamber or cylinderfor convenience indicated by the reference character X, that is, within the space in the tube part 37, and in the annular chamber indicated by the reference character Y, formed between the platenend face 36 and the block part 3S, the air is at atmospheric pressure at the instant of commencement of movement of the bolt structure 18 toward the light. AsV the latter moves toward `the right, both chambers X and Y enlarge and commence to rarefy, or lessen the pressure of, the air `within them, but they are connected together, through the airway '21, so that their actions and effects are reversibly 7 compounded to insure high speed of action to achieve the desired results.

As chamber X enlarges, it draws the air from chamber Y via the airway 21, thus insuring cushioning air flow along airway 21, and in tending to lower the air pressure in chamber Y, in which the air pressure is also being lowered because chamber Y is getting larger and larger, a substantial flow of air at good velocity takes place along the annular airway 35 which at its right-hand end is open to the atmosphere. As the bolt structure 18 accelerates in its movement toward the forward end of the receiver under the action of the spring 22, the velocity of flow of air in these annular airways 62 and 35 increases an-d the action or tendency to float the bolt structure 13, and also to keep it coaxial with the tube part 37 and the receiver 10, becomes more and more effective, and friction between moving parts becomes more and more lessened.

Furthermore, the action of the spring 22 in accelerating or moving the bolt structure 18, particularly toward or at the very end of its forward stroke when its energy of movement completes the injection of the cartridge C into the barrel 12 and impacts the cartridge C with the necessary energy to detonate it, is facilitated by materially relieving the chambers X and Y of considerable subatmospheric pressure in that both airways 35 and 62 get shorter and shorter, thus diminishing resistance to air flow therethrough; at or just prior to the moment of impact of the bolt against the cartridge, the left-hand end of the breech block part 19 reaches a point just short of the end of the tube part 37 and in effect connecting chamber X and chamber Y through a very short length of airway 62 in which resistance to air ow is thus greatly reduced, and as that is happening, the rear or left-hand end of the breech block part 19 almost reaches the slot 64 in the receiver 10 through which the sear 61 is actuated, and in that way the length of the airway 35 becomes shortened to that extent. By lengthening the slot 612- rearwar-dly, or to the left in Figure l, it can be made to serve as a port to be uncovered just before the moment of impact of the bolt structure against the cartridge, thus to insure that chambers X and Y are brought up to atmospheric pressure where it is desired, at the latter part of the tiring stroke, that the spring 22 act substantially unimpeded by differentials in air pressures. I am enabled to achieve nicety and smoothness of action by simply shortening up the airway 35, as earlier above described, making it quite short just before the bolt impacts the cartridge.

The detonated explosive propels the projectile P through and out of the barrel 12, and the reaction that results imp-els the bolt structure 18 rearwardly, or to the left, at substantial velocity and energy; this retrograde movement of the bolt structure 18 compresses the spring 22 to store energy into it for the next ring cycle and coacting with the resistance to compression of the spring 22 to bring the bolt structure 18 to a substantial gentle halt, are the chambers X and Y and the air passages 35 and 62. At the commencement of retrograde movement there is a compression of air in chambers X and Y which, as above noted, are connected through a very short length of airway 62; and a relatively sudden compression of air above atmospheric pressure commences to take place, the air seeking escape through the still short length of the outer airway 35, and thus centering of the bolt 18 relative to the receiver walls commences to take place. As the overlapping relationship between the breech block part 19 and the tube part 37' increases as the retrograde stroke proceeds, the length of airway 62 connecting the two chambers X and Y increases. Air above atmospheric pressure is forced from chamber X along the annular airway 62 to the chamber Y which, continuing to diminish in volume, continues to compress air which is thereby forced uniformly throughout the annular airway 35 to find ultimate escape to the atmosphere at the right-hand end of the breech block part 19. Both annular airways 35 and 62 are thus made to contain moving streams of air under pressure which tend to keep the parts coaxial and, in effect, to float the bolt structure during its continued rearvard stroke. Though, during the retrograde stroke, there is always air above atmospheric pressure moving toward the right in Figure l along the outer annular cushioning airway 35, the reaction of the compression chamber Y upon the inner annular airway 62 might be variable for, under the continuously changing conditions during the retrograde stroke, the tendency to equalize the air pressures in the two chambers X and Y is effected through the airway 62 and, as a result, there may be some variability of air flow therealong under pressure, but I am enabled to insure that it contains air under substantial pressure and, thus, to insure that it takes part in tending to iioat and center the bolt structure during its rearward movement.

Furthermore, both airways 35 and 62 become longer and longer as the retrograde stroke of the bolt proceeds, thus increasing the resistance to How of the air under pressure therefrom. In this manner dependable deceleration, particularly during the latter part or parts of the retrograde stroke, and bringing the bolt structure 1S to a momentary halt, are greatly facilitated. Moreover, i am enabled to bring this about while at the same time utilizing a spring 22 of materially less weight and power than would be necessary were the spring 22 to be relied upon solely. The point of momentary halting of the bolt structure 18 is just to the left of the position shown in Figure l, so that the front end of the breech block part 19 bypasses the sear 61 which, under controls later mentioned, can move upwardly through the slot 64 to enter the receiver 16 and to assume a position to hold the bolt 18 in retracted position against the action of the spring 22. The spring 22 is thus held compressed, so that when the bolt structure 1S is released by actuating the scar 61, the firing stroke of the bolt commences and the cycle above described is repeated. If the sear 61 has been precluded from catching the bolt structure 18 in retracted position, the above cycle will automatically repeat itself.

During the strokes of each cycle, the air cushioning and iioating actions above described take place, and the action of the gun is smooth and free Ifrom material or detrimental jolting; friction losses are materially lessened, and problems of lubrication materially reduced. The moving bolt structure, conveniently and simply of circular cross-section, is by itself substantially balanced dynamically in relation to its longitudinal axis and, thus, the action of the air moving under pressure in the several annular airways 35 and 62, in tending to lioat and substantially center the bolt structure relative to its coaxial stationary parts, is greatly facilitated, being aided in overcoming the factor of gravity by the inertia of high-velocity movement of the bolt during each of its strokes of each cycle. Desirably, l prefer to employ a sear construction and coacting trigger mechanism that facilitate the above-described actions, and a preferred form thereof l have shown in the drawings as including the above-mentioned sear 61. Both sear and trigger mechanism l prefer to construct as a subunit or subassembly which may be easily and quickly assembled and also disassembled from the gun structure.

This subassembly preferably comprises a casing, generally indicated at 65 (Figures l, 5, and 6), which may be made of suitably heavy sheet metal stamped or otherwise formed to provide a bottom wall 66 from which there are upstanding parallel side walls 67 and 68 (Figures 5 and 6) and also an end wall 69. End wall 69 (Figure 1) is provided with a hole "itl into which is received one arm of an L-shaped heavy lug 71 depending from the underside of the receiver 1t?, near the rear or left-hand end thereof, being secured to the receiver 10 as by welding.

Opposite the end Wall 69 of the casing 65, the latter is meca-eea'.

open-so that, afte'rrst hooking the end wall 69 onto the lug 71 and then swinging thevcasing-65 in clockwise direction to bring the upper beveled face of the side casing walls 67 and 68 (see Figures 5 'and j6) into engagement with the receiver 10, aheavy, relatively'large lug 72 (Figures V1 and 6), depending `from the Vunderside `of the receiver 1tl,enters in between thesidecasing walls 67 and 68 at their front or lright-hand end, as is better shown in Figures `1 andj 6. The lug 72 thus'forms the opposite end wall closure for the casing '65, and it has a transverse hole 73 with which holes 74 and 75 inthe side walls 67 and 68, respectively, become aligned. The hole 74 may be `threaded (Figure 6) toreceive the threaded end of a screw 76 that passes through these aligned holes and thus detachably holds the casing 65 assembled to the gun structure. I

The above-mentioned Sear-61 is of a width to tit neatly between casing side walls `67 and 68, being pivotally carried on a stud shaft thatris bridged between these side walls 67 and `68; conveniently, that `studis in the form of a stud bolt 77 (see Figure 5) which passes through a `suitable'hole 78 in the sidewall 67 and has its Vthreaded end threaded into Aa thre'adedthole 79 in the'opposite side wall 68. The sear 61 is preferably in the form of'a lever of the rst class V(see Figure 1) and has two substantially requal arms 61a and61b making an obtuse angle, as is better `shown in 'Figure 1. The sear 61 is made of any suitable metal, suitably hardenedyas may be desired. Side walls 67 and 63 hold the sear 61 centrally of the casing 65 (Figure 5) and against axial shift, while permitting freedom of pivoting, so that assembly of the casing 65 to the receiver 10 aligns the arm 61a ofthe sear with the sloti64 in the receiver 10 for movement into and out of the. path to the forward end of the breech block part 19.

Depending from the bottom'wall ofthe trigger Vcasing 65 is a U-shaped trigger -guard '80 khaving'e'nd lugs 81 and 82 provided withtcountersunk holes to receive'screws 83 and 84, respectively, which 'pass through suitably spaced holes in the casing'bottom wall 66 and 'are threaded into the base plate 85aV of an vinternal frame generally indicated at 85, whereby the two screws dependably clamp bothtrigger guard 80 `and the internal frame 85 to the casing structure. The base plate85 iits snugly between the side casing wallsV 67 and 68 and overlies substantially the entire length of the bottom wall 66, Vthusstrengthening and'reinforcing the latter. The base plate 85 and the bottom casing wall 66 have registering slots (Figures'l and 5), downwardly through which extends the `finger leverf86 of a trigger structure designatedgenerally by the reference character 87. Atthe upper end of 'the finger lever 86, the trigger structure V87 is pivotally mounted by a stud shaft in the form of a screw 88 (see Figure 5 which passes freely through the casing side wall 67 and has its threaded end threaded into the opposite side wall 68.

Spaced lengthwise along theframe plate 85a are two upstanding lugs 91 and`92 (Figure 1),ofwhich lug 91 is taller than lug 92 in order to slidably support, in down ward and 'forward inclined relation, a rod 93 that is round in cross-section, except at its forward end where it is square, as at 93a, to be slidably received in a slot 92a in the lug 92; at its rear orleft-hand end the rod 93 carries or has integrally formed therewith a head or anvil 94 which is round incross-section'and rests, for sliding support, in a correspondingly shaped hole 91a in the rear lug 91. About the rod'93 is aspring 95, one end of which abuts against the anvil 94 and the other abuts `against the forward lug 92; this action 'is to bias the rod 93-rear` wardly, or to the left in Figure `1. The `squared forward or :right-hand end 93311` of rod-93 'extends into a vertical central slot 61C inthe lower lever arm 61b of the'sear 61 to which it is pivotally connected bya` Cross-pin 96. The spring 95 thereby also biases the sear161 in clockwise direction about thepivot77. p

Parts 93--94, spring 95,.sear61,and cross-pin `9 6' can I be 4assembled as' a-subassembly tor sub-unit,*head'94 slid into hole 191a, squared end i93a-slidfdown-into slot 92a, and ipivot stud 77 thenput in'place.

The spring 95, which can be relatively light inasmuch as Iit operates .upon the sear 61 through the relatively long lever arm 61b of the sear, tends to swing the upper sear arm 61a upwardly through the slot 64 and into the inten'or of the receiver`10; during the retrograde stroke of the breech block part 19, the spring continues its abovedescribed biasing action, urging the upper end of the Ysear Varm 61a into engagement with the outer cylindrical wall of the breech block 19, and continues so to do until the block 19 bypasses the sear armi61aywhereupon the spring 95 in eifect snaps the Sear 61 further in .clockwise direction rto project the Vend ofthe `Sear arm `61a into the path of forward movement `of the breech block 19. vThe exv tent to which the sear arm 61a can thus be projected into the Vpath of the block 19 is'limited by the coaction between the Sear arm 61b and thebottomwall of the trigger casing65 which is reinforced and'strengthened by the frame base plate`85a; such limiting .action also limits and fixes the rearmost position that the head of anvil 94 can assume. The lower slotted end ofthe sear arm 611; is shaped and dimensioned to abut the 'part`85a flatwise, thus providing -a large bearing area to take up the reaction when the forward end of the breechblock 19 engages the Sear arm 61a to hold the 'breech block and bolt structure 18 inthe position shown in Figure 1 against the force of the compressed spring 22. The scar construction and mounting above described can thus dependably hold the bolt structure in retracted position and is well adapted'to take up 'and Vwithstand such minor mechanical shocks and also the force of the compressed spring 22 Vthat mayaccompany its action in holding the bolt structure in retracted position; the construction of the searpermits positioning Y of its pivot 77 relatively close to the receiver 10, and stresses exerted on the scar by the bolt structure are distributed by the reactions uponthe pivot pin 77 and the reactions between the lower sear arm '61h and the bottom wall `against which it abuts.

The round cross-sectioned anvil 94, which may be made of any suitable wear-resistant metal, has a rear end face 94a of substantial vertical height, as indicated in Figure 1, but less than the vertical dimension or diameter of the anvil 94 itself, the lower edge of the end face 94a being formed by a horizontal chord or line at which it merges, through a small` radius,'into a cam face 9411 that has a substantially at portion followed by 'a curved portion as shown in Figure l.

With these end faces of the anvil 94 coact certain structural features of the trigger :structure 87, which is better shown on a larger scale in Figure 9. The upper part of the trigger structure, which may be'made out of relatively thick flat stock, is in eifect an upstanding parallel-sided plate-like part 87a which extends rearwardly, or to the left, sufficiently -so that its lower under edge 87h can and does overhang the double bottom wall 66-85a of the trigger casing'65 (see Figure l) tothe left of the slot through which the linger-lever 86'extends downwardly, thus to provide a stop to limit the extent of counterclockwise pivoting movement ofthe-trigger structure 87 under the bias of a spring 99 showninlFigure l, and also to support, to the rear or left of the pivot 88, a pivot pin 100 which extends through a hole in the plate-like part 87a; at its ends, pin 100 pivotally supports the arms 101e and 10111 of a U-shaped detent 101 whose cross-part 101C extends crosswise of the forward or right-hand end of the vplate part 87a of the trigger structure. This cross-piece 101C, as shown in Figure 1, is thus positioned with its forward or right-hand face or edge vjuxtaposed to the rear or left-hand face 94a of the anvil 94. The detent 101 can be made ofrelatively heavy flat stock and as viewed in Figures 1 and 9, itis'biased in counterclockwise direction by a spring 102 whose upper end is received in a recess v101e formed, as by drilling, inthe underface ofthe cross-piece 101C and whose lower end is received in a recess 87e formed, as by drilling, in a forwardly projecting part 87f of the plate part 87a of the trigger structure S7. Suitable means are provided to limit this biasing action of the spring 102, conveniently by a forwardly projecting portion 87g at the upper forward end of the platelike trigger part 87a; as is clearly shown in Figures l and 9, part 87g projects over the cross-piece 101C of the detent 101 and as shown better in Figure l its forward face or edge is juxtaposed to the face 94a of the anvil 94 but is spaced rearwardly therefrom by a materialiy greater distance than the spacing of the cross-piece 101C of the detent 101 from the anvil face 94a. Since these parts, as is later explained, coact with each other to engage the anvil 94, they are preferably made of any suitable wear-resisting or hardened metal. The spring 99 (Figure l) is anchored at its one end to a suitable ear provided in the base of the frame S5, and its other end is secured to the trigger structure 87 at a point above the pivot 83 and, preferably, is connected to the detent pivot pin 100; normally the spring 99 biases and holds the trigger structure 37 in counterclockwise direction to the extent limited by the engagement of the ledge 87h thereof with the frame base plate 85a, thus holding the nger lever 86 in foremost position and ready to be manually pulled rearwardly (to the left) to swing the trigger structure 87 in clockwise direction.

As above noted, detent 101 is U-sh'aped; its parallel arms lilla and 101b are neatly received between and, re spectively, lie alongside the side walls 67 and 68 (see Figure 5), adequate clearance being provided to insure freedom and ease of both movement of translation of the detent 101 as the trigger structure is pivoted about its pivot stud 80 and swinging movement of the detent 101 about its own pivot pin 100; the casing side walls 67 and 6i; can act also to hold the pin 100 against material axial displacement.

Preferably the upper left portion of trigger part 87a is milled out as is better shown at 87h in Figure 9, in effect giving it a U-shaped horizontal cross-section by whose arms or side walls is supported the pivot pin 100 and between which extends the upper end of the spring 99 for linking to the pin 100.

The cross-piece 101C of the detent 101 (see Figure 9) has a forward contact part which is a blunt edge or narrow horizontal face 101f formed by a beveling or tapering off of the cross-piece 101C to form also an upper cam face 101g which thus merges or terminates in the blunt contact edge 101i. In the at-rest position of the parts of the trigger structure and with the bolt structure 18 held retracted by the sear 61, the parts occupy relative positions substantially as shown in Figure l; anvil 94 is in its rearmost position, fixed by the engagement of Sear arm 61h with the casing bottom wall, and the narrow horizontal contact face 1011 of the detent is juxtaposed to the lower horizontally-edged end face 94a of the anvil which, if desired, it can actually contact or engage in the at-rest position.

In actuating the finger lever 86 of the trigger structure, the operator has a choice of two ranges of movement or pull of the trigger, according as he desires to fire a single shot only `and hence put the gun mechanism through only a single cycle of injecting, tiring, and ejecting strokes, or to fire a succession of shots in rapid sequence and hence to cause the gun automatically to repeat the just-mem tioned cycle as many times as desired.

To cause the gun to fire -only a single shot, the operator pulls the trigger, at any desired speed, only part-way of its complete range of possible clockwise movement; illus tratively, the abovedescribed parts may be so proportioned that, for single tire, the trigger is pulled only halfway of its complete range of possible swing. lt has been found in practice that an operator quickly learns to control at will and dependably the part-way range of movement.

When the trigger lever 86 is pulled or swung only partway as above described, the front face 101)c of the crosspiece 101C of the trigger detent 101 moves forwardly (to the right) and as 'a result, it moves the anvil 94 forwardly by pushing against it just above the junction of the anvil face 94a with the iiat part of face 94h which makes about a angle. The front face of the detent cross-piece 101C is of small vertical dimension and its lower boundary line is at the start of the movement just about at the apex of this angle, As movement continues, the anvil 94 and its rod '93 are moved forwardly, that is, to the right, and relative pivoting between trigger part 37a and detent 101, about the axis of pin 100, takes place, bringing overhang 87g closer to cross-piece 101e; through the pin connection 96, counterclockwise swinging of the sear 61 commences and continues until the upper Sear arm 61a, whose upper end may be a bit rounded over `as shown in Figure l, is depressed enough to release the breech block and bolt structure 13, thus to commence, under the action of the stored energy in the compressed spring 22, a single cycle earlier above described. By the time the bolt structure is so released by the sear, the trigger structure has just about reached the limit of its intended range of move-ment for single-tire action, and concurrently the detent pivot has become physically elevated, and the detent crosspiece 101C (which is to the other side of the trigger pivot B) has become depressed or lowered by overhanging trigger part 37g and moved downwardly along the anvil face 94a to bring it below the apex-like junction between face 94a and face 94h and thus cause cam face 101g to coact with that apex junction to cam the detent 101 clockwise against its biasing spring 102, underneath the flat part of anvil face 94b. This happens with a snap action. In this manner, though the trigger lever 86 be now held in its 4midway position, or even slightly moved further, the anvil-actuating trigger detent 101 is cammed out of the path of retrograde movement of the anvil 94 and rod 93; the spring 95 is thus freed to bias the scar 61 in clockwise direction to catch and hold the bolt structure 18 at substantially the end of its retrograde spring-compressing stroke, thus halting the gun mechanism at the end of a single cycle. Bolt spring 22, now compressed, acts through the scar-stopping engagement of scar arm 61h with the casing bottom wall to iix the rearmost position of the anvil 94, detent cross-piece 101C still being underneath the anvil 94.

Subsequent release of the finger lever S6 from this illustrative midway position lets the spring 99 swing the trigger structure 87 counterclockwise to its 'at-rest position; during such swing, the detent cross-piece 101e moves rearwardly and cams itself, under the action of its spring 102 and by the coaction of its cam face 101g and the anvil cam face 94h, back into its normal position juxtaposed to the rear end face 94a of the anvil 94, as shown in Figure l. All is now ready for a subsequent 'actuation of the trigger.

For continuous and automatic repeat fire, the operator gives the trigger structure 87 its full or complete range of swinging movement, a range which, desirably, is limited by the engagement of the linger lever 86 with the rear arm of the trigger guard S0. When this is done, the trigger detent 101 pushes against the anvil face 94a as before, and as the movement continues and the detent 101 becomes more and more depressed by the overhang 87g as the latter tilts about the trigger axis 0S, the detent crosspiece 101e again moves downwardly along and snaps ofi the anvil Acam face 94h and its cam face wig cams it underneath the anvil 94, but because the range of swing of the trigger structure and the tilting of these parts thereof that lie above the trigger pivot 88 are greater, the forwardly projecting part 87g of the trigger structure is brought into engagement with the anvil face 94a immedia'tely after detent 101 has snapped od it and part 87g now holds the anvil 94 and its push rod 93 in forwardly-moved position, blocks it against lmaterial retrograde movement, and thus maintains the upper sear arm 61a depressed so that it cannot catch `and hold 'the bolt structure; the latter and coacting mechanism, therefore,

` have to operate in atsuccessio'n of cycles, eachcycle comprising cartridge injection, firing, and shell ejection.

Cyclic repetition continues for as `long as the trigger structure 87 is held in maximum depressed or actuated position; release vof the ngerl lever 86 during Iany one of such cycles swings the upper trigger structure part 87g rearwardly, or to the left in Figures 1 `and 9, thus freeing the anvil 94 and push rod 93, for retrograde movement under the action of the spring 95 to thereby bias the sear 61 to `catch and h-old the bolt structure 18 at the end of the selected cycle; such manual release of the trigger structure ifects a restoration ofthe trigger detent 101 to its normal position as shown inthe drawings, whence the mechanism is again ready for selective firing according simply to the range lof trigger movement to be effected manually.

If desired, the operator may manually set a suitable stop to make sure that lhe does not pull thetrigger beyond the `single-tire range of movement, and thisfeature,fabout to be described, is of advantage in training personnel. For this purpose I provide in the thickened part of the rearmost vertical arm of the trigger guard 80, where it merges into the receiving lug 81, a stop member in the form of a suitably heavy lug 104 that is secured Iat right angles to a short shaft 105 pivotally carried in the arm of the trigger guard 80; an outer extended and shouldered end 105e of the shaft 105 carries la thumb lever 106 by which the stop lug 104 may be swung into or out of the path of rearward swing of the finger lever 86 of the trigger structure 87. v

Parts 104, 105, and 106 are assemble/das a unit and as such are insertable into position on the trigger guard before the latter is'secured tothe trigger casing 65. The rear arm trigger guard 80 is lmilled out or recessed ccntrally 'as at 80a, leaving two spaced side walls in one of which is a bearing hole 80b to 'receive the free end 'of shaft 105 and in the other is a companion bearing `80c slotted as shown to be open from above, thus to permit the stop lug 104'to slide through asthe sub-unit is axially slid to enter the free vend of shaft 105 into bearing hole 80h.

The slotted or open bearing 80e permits ease of drillingra hole '80f in which is inserted a spring 80g and to receive a ball 80h above the spring, both being held in place by the overlying shaft 105 when the latter is slid into place. Shaft 105 hastwo curvedrecesses 105b and 105C, somewhat less than half-spherical in shape to coact alternatively with'the ball 80h as the shaft is turned by the thumb lever `106, and thus to `releasably hold the shaft ineither of two positions; in one of them, stop lug 104 is housed in the recess 80a and thumb-piece v106 stands up alongside and snugly against the trigger casing wall A68 whose bottom wall 66 overlies and just contacts the shouldered part 105e ofthe vshaft 105 to hold the latter down in its curved bearing seat 80c, 'and in the other position, stop lug 104 stands displaced about 90 and is about horizontal `(Figure l) with its end in the path of movement of trigger finger lever 86 while linger-piece 106 `stands projected rearwardlyof thetrigger guard where it can be easily and quickly engaged by a linger or the thumb to swing it upward and out of trigger-limiting position. Thus the shift from singlere to automaticsuccessive firing can be quickly achieved, should the operator have chosen initially to set the trigger stop lug 104 to single-tire position.

The assembly of the trigger guard 80 to the casing,N

as by the screws 82 and 83 as abovedescribed, in effect completes the assembly ofthe sub-unit 104, 105, and "106 and of spring 80g and ball 80h to the gun for thereby the lslotted or'open `bearing 80e is closed oif and the underside of the bottom wall66 of the trigger housing 65 preventssuch swing of the shaft 105 as is needed to align stop-lug 104 with the slotted bearing lll 80e; without such'alignment, the sub-nit'104, '105,- 106 cannot 'be Vslid outV `of its bearings. f

. The above-described sear and trigger mechanism makes possible, also), simple provision for locking the mechanism in a safety condition, that is, to lock it against firing should the trigger lever 86 be accidentally pulled. As above described, the bolt 'structure 18 is 'held in retracted positionV and the spring 22 held in compressed condition by the scar 61 which, Vthrough the widelyspa'ced pivot 77 and the abutting of 'its lower lever arm 61h against the 'trigger housing bottom wall, distributes the resultantstresses. Forwardly of thevlower sear arm 61b, and provided with suitable bearing holes vin the parallel side walls 67 and 68 of the trigger casing '65, I provide a shaft'orV pin 110 (see Figure 1) provided with a thumb lever 11.1 secured thereto at one outerV end of the shaft-110 so that the thumb lever 111 can be swung alongside and externally 'o f one of the casing side walls, such as the'side wall 68 (see-Figure 55).' Inbetween the casing sidewalls 67 and 68, the-shaft v-110 has secured to it a stop arm` 112 which is shaped and dimensioned so that when swung' by the shaft 110 in counteelockwise direction (Figure l), its squared-off end face engages the forward front edge face of the lower sear arm 61h when the sear is in bolt-holding Vposition, the frame plate/85a serving as a stop to'limit the counterclockwise movement of the stop arm V112. In that position of Vthe stop arm 112, the thumb lever 1171 may conveniently stand in upright position externally of the 'trigger casing, as indicated in Figure l. position of the stop arm 112, the Sear 61 is-dependably locked against counterclockwise swinging and, thus, the sear cannot be actuated until, by means of the thumb lever 111, the stop arm 112 is swung clockwise for about ninety (90) Vdegrees and out ofthe path of actuating movement of the sear. Any suitable means, such as the frictionV of the part-s, may be employed to hold theY safety mechanism in its two positions of selective actuation.

The above-described selectively actuated trigger and Sear mechanism is capable of embodiment in rugged-and durable form without detrimentally affecting either sensitiveness of actuation, control of selectivity, or smoothness 'and ease of operation of the gun under varying conditions of practical use; and coacting therewith, to facilitate achievement of these advantages, is the air-cushioned movement of thebolt structure during its strokes of movement. VViolent or detrimental jarring or jol-ting of the gun structure as a whole is avoided not only by the substantially air-floated movement of the relatively heavy bolt structure, but also by the smoothness of control of changes in velocity of movement of the bolt structure during its successive strokes. For such reasons as these, also, sighting or aiming of the gun structure is greatly facilitated and better accuracy achieved. At the Vforward end of the gun barrel 12 I provide a front sight, indicated apt-* in Figure l, and at the rear end of the gun'structure 'I provide an adjustable rear sight 116 which, for such reasons as the above, can also be made more compact and lighter in construction while maintaining it sufficiently rugged and strong.

The rear sight 116 (Figures l and 2) comprises a disklike part 117, provided with a sight hole 118, and is integrally formed or secured to a flat Velongated part l119 having a front or right-hand face (Figure l) that is flat so that it can rest against the smooth flat face 38a at the rear of the heavy block part 38 that closes the rear end of the receiver 10 (see also Figure 4). It is held assembled to the block part 38 by a U-shaped, casing-like, metal stamping 120 which is flanged, as at 12011 and 120b (Figures 2 and 4), and with the flanges resting against the rear face 38a of the part 38, suitable screws 121, that pass through the flanges and are threaded into theblock part v38, secure the part 120 in place to form a vertical channel or guideway in which the part 119 `of the rear sight'issnugly-received. The parts areso assembled that In that Y the vertical axis of the part 119, with the sight hole 118 on that axis (see Figure 2), coincides with a vertical diameter of the receiver.

The rear face of the sight part 119 is provided with a suitable number of suitably spaced transverse of horizontal slots 122 which, according to the manually selected vertical position of the rear sight 116 relative to its channel or guideway, coacts selectively with Ia detent 123 formed by bending over one end of a long leaf spring 124 that lies against the vertical wall of the part 12C and Whose lower end is anchored by a screw 12S (Figures 1 and 2) to the block part 3S. Screw 125 also passes through the casing part 120 and -aids in holding that assembled to the block part 38.

Accordingly, by grasping the part 117 of the sight 116 (Figures l and 2), the sight 116 may be given any desired vertical position in relation to the front sight 115, the spring detent 123 yielding out of any one slot 122 and snapping into the selected slot to thereafter releasably hold the sight in the selected position for the desired range.

Should the gun have to be disassembled, as by removing the locking pin 50 (Figure l), in the manner above described, so as to permit withdrawal of the member 40 of which the closure block 38 is a part, the rear sight just described above remains carried by the part 40 and thus does not become an impediment in the further dismantling of the gun structure, as it might were it to be carried directly by the receiver 10. Upon the removal of the part 40, thus opening the rear end of the receiver 10, the bolt structure 1S may be readily slid out of the receiver.

Preferably suitable means are provided to hold the bolt structure 18, during its strokes of movement within the receiver 10, against rotary movement in order to maintain the proper relationship between the ejector 30 (Figure l) and the slot 31 in the bolt 20, and preferably this means comprises, as is better shown in Figure 7, two small guideways 127 and 123 that extend longitudinally in the exterior surface of the breech block part 19, and two elongated guide bars 129 and 130 mounted in the wall of the receiver 11b to project inwardly thereof for reception, respectively, into the guideways 127 and 12S. The guide bars may be set into slots 12961 and 130a, respectively, milled in the receiver wall and they may be secured therein in any suitable way, as by welding externally of the receiver 10. They may be relatively short.

Preferably, as shown in Figure 7, the guideways 127 and 128 are equally spaced to either side of the vertical axis of the breech block part 19 so as to have minimum effect upon the dynamic balance of the bolt structure. They are located not on a diameter of the breech block 19, but rather on a horizotnal chord thereof, illustratively just above the horizontal diameter as seen in Figure 7, and the guide bars 129 and 1311, of course, are similarly located in the receiver wall on a chord; this just-described relationship makes it impossible to insert the bolt structure 13 into the receiver 1@ in a position rotated 180 degrees from the position shown in Figure 7 for in such case the guide bars 129 and 1311 and guideways 127 and 128 would not register. Accordingly, insertion can be effected only so that slot 31 is always aligned with the ejector pin 30.

The guideways 127 and 12S and the guide bars 129 and 134i are preferably made of relatively small crosssection and are respectively intertted to provide an easy sliding tit; close manufacturing tolerances can here be departed from because yof the centering action of the air under pressure in the airways 35 and 62 as above described. The cross-sectional area of the annular airway 35 and that of the annular airway 62 are relatively large, and the guideways 127, 128, substantially closed for air flow by the guide bars therein, need not in that respect affect the air-cushioning action of these airways as above described. Moreover, the guide bars and guideways coact in any at-rest position of the bolt structure to restrict side-play between the bolt structure and the interior wall of the receiver 10 and can serve to hold the breech block part 19 of the bolt structure substantially coaxially with the receiver 10 and the tube part 37 in spite of the relatively large radial dimensions of the two annular airways 62 and 35, and in thus maintaining substantial concentricity of the opposed cylindrical walls that form the annular airways 62 and 35 in at-rest positions, they serve advantageously to precondition such airways for subsequent air-floating action on the moving parts.

These latter actions of maintaining substantial concentricity of the parts in at-rest position are achieved, because of the above described location of the radial guideways (127 and 128) and guide bars (129 and 130) on a horizontal chord relaitvely close to but spaced from the horizontal diameter, by a cradling action akin to that achieved by placing the cables of a suspension bridge closer together at the center of the span than at the supporting towers whereby the roadway is substantially always centered (against side sway) by equal and opposed horizontal force components.

Where the guide bars 129 and 130 are relatively short, l prefer to position them in the receiver wall near the forward end of the breech block part 19 when the bolt structure 13 is in retracted position as shown in Figure l; such a location places them with their midpoints approximately at the vertical transverse plane through the center of mass of the whole bolt structure 13, thus approximating a balancing support. The above-mentioned concentricity of the opposed cylindrical walls that form the annular airways 62 and 35 need not, in the position of rest of the bolt structure 13, be geometrically perfect, and a reasonable approximation thereto suffices to precondition the parts in aid of the subsequent action of the air moving through these airways in providing quickly dependable air cushioning or air-floated movement of the bolt structure relative to the stationary parts. In the position of rest of the bolt structure 18, in which it is held by the sear 61, the actions of the spring 22 and the sear 61 on the bolt structure are in respective directions to tend to aid in this pre-conditioning action, for the line of action of spring 22, being coaxial with the bolt structure 18, is above the point (as seen in Figure l) at which the breech block part 19 is contacted by the sear 61; the action of the spring 22, therefore, is to tend to tilt the bolt structure 18 about the just-mentioned point, acting clockwise as viewed in Figure l, and thus it tends to counteract the effect of the weight of the left-hand portion of the breech block part 19, acting about a transverse axis through the midpoints of the guide bars 128129, to tend to tilt the bolt structure in counterclockwise direction, particularly where the guide bars are of very short length. lt is thus possible to substantially balance these opposing moments as will now be clear, and hence the guide bars can be made short.

The bolt structure 18 may be manually brought to its retracted position and the spring 22 compressed by means of a retractor that comprises an L-shaped element 133 (see Figure 8) that has a long arm 133a that is of trapezoidal cross-section, as is better shown in Figure 7, its longitudinal side edges are beveled off or inclined to provide this cross-section; at its forward end the part 133 has a short arm 133b which projects downwardly into the receiver 10 and into the path of forward movement of the front end face of the breech block part 19. The retractor arm 133b is held movably in this position in that the elongated part 13361, which has a thickness slightly less than that of the wall of receiver 1Q, is slidably received in a slot 135 in the receiver wall, the slot, as is better shown in Figure 7, having inclined side walls to give it a trapezoidal cross-section smaller to that of the part 133a; the latter is inserted into the slot from Figure 8.

17 the inside of the receiver tube 10, the beveled or inclined edges of the part 13311 and of the slot 135 holding it against movement radially outward and forming coacting guiding surfaces whereby the member 133 may be moved back and forth along the slot 135.

As is indicated in Figure 8, the slot 135 is of such a length that the retractor part 133b has a stroke of movement greater than the stroke of movement of the bolt structure 1S and is so located that when the bolt part 20 is in forwardly projected position as when it strikes a shell in the barrel 12, the retractor part 133a is positioned at the forward end of the slot 135 which brings the retractor part 133b well in advance of the foremost position of the front face of the breech block part 19. The slot 135. extends rearwardly a suflcient extent so that sliding rearward movement of the part 133a brings the retractor part 133b into engagement with the breech block part 19 and moves' the latter rearwardly against the actionof spring 22 to aV position appropriate to permit the sear 61 to catchand hold the breech block part 19 in a retracted position and, hence, in readiness for tiring control by the trigger mechanism, as above described.

I maintain the slot 135 covered throughout its length and hold'the member 133 in proper coacting relation to the slot 135 by means of an elongated-cover plate 136 (Figures 7 and 8) which is of a width greater than that of the slot 135, as is better shown in Figure 7, and externally of the cover plate 136 I provide a'relatively heavy finger piece 137 which may be fabricated as a separate piece and provided with a base plate 138 that rests against the cover plate 136 at about the midpoint of the latter. The three parts 133e, 136, and 138 are secured or clamped together by any suitable means, as indicated at,140,ir1

` In the forward position of the bolt structure, Vthe rear As earlier above mentioned, a relatively heavy mem- Y ber 11 (see Figure 1) ismounted in the forward end of the receiver 10 and has mounted init the-rear end of the barrel 12. I am enabled to give this member 11 a simple `configuration and thereby greatly facilitate its manufacture, and also to expedite its assembly in relation to other parts of the gun construction due to certain coactions. So far as I am aware, it has heretofore been impossible in prior 'gun constructions to achieve such a simplification as I have in this member 11. Y

As shown in Figure 1, the earlier above-described .shoulder V14 is formed by the forward or right-handrpo'r- Vtion of a tapered orA frustoconical b ore or turning 142 Whose smallest diameter is greater than the diameter of the flange part F of a shell C so that that flange part can Vtake up against the rear end face of the barrel 12, and its larger diameter is considerably less than the inside rdiameter of the receiver 10. Illustratively, the taper may `be of the following order: the two diameters of the tapered Ybore 142 are respectively 0.643 inch and 1.125 inches and Y the part can be fabricated in a screw machine. In prior constructions intricate configurations have had to be provided to form guideways or the like to guide a shell into or out of coacting relation to the gun barrel 12, and such configurations have had to be made in large measure by costly methods of fabrication.

With this frustoconical bore or mouth 12 coact the bolt 20 for cartridge injection and the ejector pin 30 for ejecting the Aemptied shell and ipping it laterally and downwardly Vthrough the extractor opening 29 above described. The discharge opening 29 is just to the rear (to the left, as viewed in Figure l) of the tapered mouth 142 of the part 11, and just forwardly of the ejector pin 30, so that as the empty shell is tilted off the rapidly retracting bolt structureto swing downwardly and out of the discharge opening 29, the large end of the tapered mouth 142 insures large clearance for this tilting and nipping discharge movement of the shell and, moreover, provides such arnple clearance so that various Vlengths of shells may be employed in the cartridges that the gun can handle.

For injecting a cartridge into the rear end of the barrel 12 I provide the rectangular opening 144 (Figures 1 and'll) in the receiver wall 10, and in Figure l is better shown the relationship of this opening to the mouth o f `the tapered bore 142 and to the bolt 20 of the bol-t structureV 18 in retracted position. The opening 144 is posiltioned laterally, as is better shown in Figure l1, and may be provided with a rectangularly lcross-sectioned, openlended casing 145 which may be separately fabricated and weldedor otherwise secured to the receiver 10. In crosssection the part 145 is dirnensioned to receive a magazine generally indicated in Figure 11 at146, and this may be of any suitable sheet metal construction, beingv provided with a usual type of spring 147 acting upon a pushY plate 148 which, in turn, acts upon a suitable number of car- `tridges C to urge them in a direction toward the right as viewed in Figure 11, suitable means being provided to hold the inserted magazine 146 in such a position that its two opposed walls 149 and 150, made of any suitable spring sheet metal, are held so that their spaced ends just clear the path of movement of the bolt 20. These two spring end walls 149 and 150 hold .the foremost one of the series of cartridges C in the magazine in a position indicated at Clin Figure 1l, a position in which a portion of the cartridge is actually in the path of forward movement of the front end of the bolt 20.

As the -bolt 20 moves forwardly at'good velocity, it strikes the projecting portion of the cartridge C1 and commences to impel it toward the barrel 12 (see Figure l), but any tendency of the impelled cartridge C1 to tilt-is counteracted immediately by the entry of the nose of the Vshell into the large mouth of the tapered bore 142 o-f the part 11 which thereupon guides the cartridge into the gun barrel,.as above described.

I have found in practice that, due to the pneumatic action which, in the above illustrative embodiment, is effectedby the coacting or compounding action of the air chambers X and Y, the action of the gun both 'in single firing and in automatic successive tiring is smooth and greatly facilitates manual handling and aiming of the -gun when tiring. Uncomfortable Vjolting and violent jarring are avoided, advantages that contribute toward better trigger control in shifting from single tiring to automatic successive tiring and that make for improved marksmanship. Moreover, I have found in practice that, due to `certain features of the Vpneumatic action, a gun constructed according to my invention functions satisfactorilyrand etli- .ciently with cartridges, whether of the same calibre or of different calibres, that develop substantial differences in gas pressure upon detonation. For example, `I have operated a gun so constructed with cartridges that develop gas pressures from approximately 20,000 pounds per square inch to approximately 36,000 pounds per square inch, all ,without detriment to the achievement :of `the many adt9 vantages such as those above mentioned; within the juststated range of developed gas pressures fall the two abovementioned differently calibred cartridges, namely, the 45 calibre Colt and the 9 mm. Parabellum cartridge, and also the high-pressure 9 mm. Parabellum cartridge which develops on the order of 36,000 pounds per square inch of pressure, and I have successfully operated such a gun by using in it, interchangeably, these three different cartridges.

In other words, without having to change the bolt structure 18 which, for the just-mentioned cartridges, can have a weight of one pound and six ounces, and without having to change the spring 22 or to alter the dimensions of the airways 62 and 35, the gun operates efficiently and achieves the above-mentioned advantages, with the aforesaid calibres of cartridge and range of developed gas pressures. The gun, therefore, has a substantial range or capacity and is in effect self-adapting to such wide range; and the self-centering of the bolt under air pressure and the air-floated movement of the bolt structure, also take place throughout such range.

In these connections, as I now understand the functioning of the gun construction of my invention, I believe that reversibility of air ow between the two air chambers 'X and Y duringT either stroke of the bolt structure, contributes toward this wide range of self-adaptability. For example, as the retrograde stroke proceeds, the rate of change of volume for chamber X is different from that for chamber Y, and toward the end of the retrograde stroke, the volume of chamber X is greater than that of chamber Y; at one portion of the retrograde stroke, air can be forced not only along airway 35 to the atmosphere, but also along airway 62 into chamber X, and at a later portion of the stroke, close to the end, the effect of the larger volume of air under pressure in chamber X can force air along airway 62 into chamber Y for ultimate escape to the atmosphere through airway 35, thus achieving nicety and cushioning of halting of the breech block bolt structure. If the breech block structure is not caught by the sear, so that a forward movement thereof at once commences, air under compression in both chambers X and Y, and principally in chamber X, can actually aid the spring 22 in starting the forward movement of the bolt structure, bearing in mind that these actions take place at considerable rapidity. As the forward movement continues and the air in chambers X and Y reaches atmospheric pressurel the continued forward movement of the bolt structure commences a rareiication of the air in these chambers and a retarding or dragging effect upon the forward bolt movement is counteracted, first, by the relatively large volume of air in chamber X, aided by the smaller volume of air in chamber Y, and, secondly, by ingress of air, as the forward movement progresses, by way of airway 35. These actions during both strokes, I find, are not detrimentally affected by such changes in energy for impelling the bolt structure in its retrograde stroke as accompany the reactions caused by the detonation of cartridges that evolve different gas pressures such as those above mentioned.

In any event` I have achieved the above advantages and results within the above-mentioned range of calibres or gas pressures where the gun construction has dimensions, Vin addition to those mentioned above, as follows: Where the outside diameter of the breech block part 19 is 1.374 inches and its inside diameter is on the order of 0.818 inch,

the radial dimension of the airways 35 and 62 can be on the order of about 0.004 inch, the length and other dimensions of the parts that form the chambers X and Y, as viewed in Figure l, being substantially proportional to the just given diameters of the breech block part 19.

The gun provided by this invention will be seen to be strong and durable in construction, well adapted to meet 'the conditions of hard practical use, is eiiicient and dependable in its action and control, and otherwise meets the 20 various objects heretofore set forth and achieves many advantages in manufacture, maintenance, care, and use.

As many possible embodiments may be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be` understood that all matter hereinabove set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

I claim:

l. A gun construction comprising a receiver having a gun barrel at one end thereof, a bolt structure having a cylindrical breech block part cf lesser diameter than the bore of said receiver by an amount materially greater than that needed to provide a sliding iit and thereby form an annular airway therebetween and having a bolt projecting forwardly therefrom to impact a cartridge in said gun barrel and to impel the bolt structure rearwardly, by the reaction thereon of the detonation of the cartridge, said breech block part having a cylindrical bore open from its rear end, thereby providing in the latter an annular piston face, means closing and substantially sealing off the rear end of the receiver and supporting a forwardly projecting part of round cross-section that is entered into the bore of said block and that has an outside diameter less than the diameter of the bore of the block by an amount materially greater than that needed to provide a sliding tit and thereby to form an annular airway of relatively large radial dimension, said forwardly projecting part forming with the closed forward end of the blockfbore and with the cylindrical walls thereof a chamber of substantial variable volume according as its axial dimension changes during strokes of movement of said block part, said annular airway always maintaining an air-flow connection between said variable-volume chamber and the annular chamber to the rear of said annular piston face and said first-mentioned annular airway forming the only communication, during said strokes of movement of the bolt structure, between said annular chamber and the atmosphere whereby upon reciprocation of said bolt structure air is drawn from the atmosphere and moves at substantial velocity along said annular airways as said chambers are elongated during the forward stroke of the bolt structure and air under pressure moves along said airways as said chambers lessen in volume during the retrograde stroke of the bolt structure to substantially air-float the latter concentrically relative to said receiver, means for releasably holding said bolt structure in retracted position, and spring means that is stressed in vresponse to the retrograde stroke of the bolt structure 'and eXpends the energy thereby stored therein to impel -the bolt structure in forward direction.

2. A gun construction comprising a receiver having a gun barrel at one end thereof, a bolt structure having a cylindrical breech blocl; part of lesser diameter than the bore of said receiver by an amount materially greater than that needed to provide a sliding t and thereby form an annular airway therebetween and having a bolt projecting forwardly therefrom to impact a cartridge in said gun barrel and to impel the bolt structure rearwardly, by the reaction thereon of the detonation of the cartridge, said breech block part having a cylindrical bore open from its rear end, thereby providing in the latter an annular piston face, means closing and substantially sealing off the rear end of the receiver and thereby coacting with the walls of the receiver, throughout the strokes of movement of said breech block part, to close olf communication oetween the atmosphere and the space to the rear of said annular piston face except by way of said annular airway, said means supporting a forwardly projecting cylindrical part that enters said bore and that is of lesser diameter than the bore of said breech block part by an amount materially greater than that needed to provide a sliding iit With said bore and thereby forman annular airway therebetween that connects the chamber of said bore with the annular chamber to the rear of said annular piston face whereby upon reciprocation of said bolt structure air is drawn from the atmosphere and moves at substantial velocity along said annular airways as said chambers are elongated during the forward stroke of the bolt structure and air under pressure moves along said airways as said chambers lessen in Volume during the retrograde stroke of the bolt structure to substantially air-float the latter concentrically relative to said receiver, the chamber formed by said bore and said cylindrical part being, when said bolt structure is substantially at the Vend of its retrograde stroke, of greater volume than said annular chamber, means for releasably holding said bolt structure in `retracted position, and spring means that is stressed in response to the retrograde stroke of the bolt structure and expends the energy thereby stored therein to impel the bolt structure in forward direction.

3. A gun construction comprising a receiver having a gun barrel at one end thereof, a bolt structure having a cylindrical breech block part of lesser diameter than the bore of said receiver by an amount materially greater than that needed to provide a sliding tit and thereby form an annular airway therebetween and having a bolt projecting forwardly therefrom to impact a cartridge in said gun barrel and to impel the bolt structure rearwardly, by the reaction thereon of the detonation of the cartridge, said breech block part havinga cylindrical bore open from its rear end, thereby providing in the latter an annular piston face, means closing and substantially sealing-oif theV rear end of the receiver and supporting a forwardly-projecting part of round cross-section that is entered into the bore of said block and that has an outside diameter less than the diameter of the bore of the block by an amount materially greater -than 'that needed to provide a sliding vfit and thereby to form an annular airway of relatively large radial dimension, said forwardly projecting part forming with the closed forward end of the block bore and with the cylindrical walls thereof a chamber of substantial variable volume according as its axial dimension changes during strokes of movement of said block part, said annular airway always maintaining an air-flow connection between said variable-volume chamber and the annular chamber to the rear of said annular piston face and said iirst-mentioned annular airway forming the only communication, during said strokes of movement of the bolt structure. between said annular chamber and the atmosphere whereby upon reciprocation of said bolt structure with accompanying changes in the volumes of said two chambers air is interchanged between them through said second annular airway and is interchanged with the atmosphere through said first annular airway at velocities and pressures to substantially air-float said bolt structure concentrically to said receiver, means for releasably holding said bolt structure in retracted position, and spring means that is stressed in response to the retrograde stroke of the bolt structure and expends the energy thereby stored therein to impel the bolt structure in forward direction.

4. A gun construction comprising a receiver substantially closed oi at one end and having a gun barrel at the other end thereof, a bolt structure reciprocable within 22 said receiver and having a cylindrical breech block part of a diameter less than the inside diameter of the bore of said receiver by an amount materially greater than that needed to provide a sliding iit and thereby to form an annular airway therebetween of substantial air-ow capacity for communication, during the strokes of said bolt structure, between the atmosphere and the interior of said closed-off end of the receiver and havinga bolt of lesser diameter than that of said breech block and projecting forwardly therefrom to impact a cartridge in said gun barrel and to impel the bolt structure rearwardly by the reaction thereon of the detonation of the cartridge and to compress air in the chamber formed by said breechV block part and receiver for escape through said airway, spring means that is stressed in response to the retrograde stroke of the bolt structure and expends the energy stored therein to impel the bolt structure in forward direction to draw air through said annular airway from the atmosphere and into said chamber, whereby said bolt structure is substantially air-oated during its strokes of movement, said airway being of relatively large radial dimension for airfloating action upon said block part during reciprocation thereof, means operating upon said block part when said bolt structure is in retracted position to hold said block part substantially coaxial with said receiver in order thereby to prevent the weight of the block part from detrimentally shifting the latter radially downward into a position of tangency with the bore of the receiver and thereby substantially maintain the annular cross-section of the airway in readiness for air-oating action when movement of the bolt structure commences, said means comprising circumferentially spaced coacting elements positioned above the central horizontal plane through the receiver and equiangularly spaced from the vertical aXis of the receiver, said elements projecting inwardly from opposite sides of the receiver and within the range of reciprocation of the breech-block part for direct engagement with and thereby substantially cradling said breechblock part substantially .coaXially with said receiver, means for retracting said bolt structure to stress said spring means and store energy therein including means for holding said bolt structure in retracted position, and means for controlling said holding means.

References Cited in the file of Ythis patent UNITED STATES PATENTS 836,502 Johnson Nov. 20, 1906 908,294 Marga Dec. 29, 1908 1,297,240 Pritchett Mar. 11, 1919 1,446,388 Ludorf Feb. 20, 1923 1,484,163 Vincon Feb. 19, 1924 2,049,776 Hyde Aug. 4, 1936 2,072,197 Bergmann Mar. 2, 1937 2,079,039 Razee May 4, 1937 2,447,091 Pope Aug. 17, 1948 2,492,815 Robinson Dec. 27, 1949 2,539,554 Sampson et al. Jan. 30, 1951 2,548,622 Sampson et al Apr. 10, 1951 FOREIGN PATENTS 359,414 Germany Sept. 21, 1922 

